FIG. 23 is a perspective view showing a configuration of a conventional capacitor unit of this kind; and FIG. 24 is a perspective view showing a circuit board used in the capacitor unit. In FIGS. 23 and 24, circuit board 501 is provided with mounting holes 501a into which lead wires 502b and 502c of capacitor 502 pass through. On the edge of the capacitor unit, attaching holes 501b for attaching the capacitor unit are provided. Capacitor 502 has a configuration in which a capacitor device (not shown) impregnated with driving electrolyte is housed in metal case 502a having a cylindrical shape with a bottom, and extracting lead wires 502b and 502c for external extraction is extracted as a pair of electrodes from this capacitor device.
The thus configured conventional capacitor unit is electrically connected to a circuit (not shown) provided on circuit board 501 by fitting pair of lead wires 502b and 502c of capacitor 502 into mounting holes 501a provided on circuit board 501 and then soldering the rear surface side thereof. In this way, a plurality of capacitors 502 are mounted on one circuit board 501.
Then, for use, attachment to a case or equipment to be used is carried out by screw-fixing via attaching holes 501b provided on circuit board 501.
Note here that prior art document information as to such a conventional technology is disclosed in, for example, Japanese Patent Unexamined Publication No. H06-275471.
Recently, from the viewpoint of conservation of global environment or improvement in fuel consumption, hybrid cars or electric vehicles have been rapidly developed. Furthermore, various functions for controlling vehicles have been rapidly electronized. Braking of vehicles is also being shifted from a conventional mechanical hydraulic control to electric hydraulic control, and various electric braking systems are proposed.
When an important function such as brake is out of order because voltage reduces in a battery used as a power supply or certain contingencies occur and power is not supplied, hydraulic control cannot be carried out. Therefore, a redundant system using an emergency power supply is often configured.
Conventionally, a method using another battery as an emergency power supply has been proposed. However, battery has a characteristic of deteriorating over time and its expected lifetime is at most five years when it is used for a vehicle.
Furthermore, it is difficult to detect deterioration in the process and to exhibit a function as an emergency power supply when certain contingencies occur.
Recently, as an emergency power supply substituting for a battery, much attention has been focused on a capacitor such as an electric double layer capacitor. When a capacitor is used in a way in which, for example, charging is carried out when a system is operating and discharging is carried out when a system is not operating, the lifetime of the capacitor can be extended to several times as the lifetime of a battery. Therefore, it is said that a capacitor can withstand the use for 15 years, that is, a target lifetime of a vehicle.
Note here that prior art document information as to such a conventional technology is disclosed in, for example, Japanese Patent Unexamined Publication No. 10-189402.